Just purchased a new, never fired Benelli M4. Stock tube holds 5 rounds of Federal Power Shok 2-3/4 00 buck just fine. Attached DMW 2 round add-on extension, DMW part 011. Inserted DMW mag spring that came with the extension. Tried to load the extended magazine, and cannot get last 1/4 inch of 7th shell into the magazine. Replaced the DMW mag spring with the stock Benelli mag spring, thinking the DMW spring was too long and needed to be shortened. Still cannot get that 7th shell into the magazine, even with the shorter stock spring in place.
Any suggestions? Perhaps the Federal shells are slightly longer than other 2-3/4 shells, and that is the problem. Or, does the DMW mag extension have a design flaw?
